DNA Replication, Transcription, and Translation Explained

Posted on Mar 12, 2025 in Biology

DNA Replication, Transcription, and Translation

Understandings:

The replication of DNA is semi-conservative and depends on complementary base pairing.

  • Complementary base pairing ensures two identical DNA strands are formed after replication is complete.
  • In replication, the original strands are used as templates, allowing complementary bases to be added according to base pairing rules.
  • DNA replication is semi-conservative, meaning the new DNA that is created consists of one old strand (template) and one new strand (synthesized strand).
  • The significance of complimentary base pairing means that the two daughter cells have the exact same DNA genome as the parent cell.
  • Gene sequences (if no mutations occur) are therefore successfully passed on from generation to generation.
  • Adenine is always matched with thymine with two hydrogen bonds, and guanine is always matched with cytosine with three hydrogen bonds.

Skill: Analysis of Meselson and Stahl’s Results

Analysis of Meselson and Stahl’s results to obtain support for the theory of semi-conservative replication of DNA.

  • Read through the article for obtaining evidence for the theory of semi-conservative replication and complete the data-based question on the analysis of Meselson and Stahl’s results on pages 113 and 114.

Helicase and DNA Unwinding

Helicase unwinds the double helix and separates the two strands by breaking hydrogen bonds.

  • The DNA strand is unwound and separated by an enzyme called helicase.
  • The separation is completed by breaking the hydrogen bonds between the base pairs.
  • Energy from ATP is required for Helicase to move along the DNA and break the bonds.

DNA Polymerase and Nucleotide Linking

DNA polymerase links nucleotides together to form a new strand, using the pre-existing strand as a template.

  • Free nucleotides found in the nucleus are added to the strands of DNA by an enzyme called DNA polymerase.
  • DNA polymerase brings the nucleotide into position so a hydrogen bond can form between the base pairs.
  • A covalent bond is formed between the phosphate on the free nucleotide and the sugar on the existing chain.
  • Nucleotides are added to complimentary bases on the DNA template strands according to base-pairing rules (adenine pairs with thymine and guanine pairs with cytosine).
  • Bases are added in one direction on one strand and are added in the opposite direction on the other strand.
  • Very few mistakes occur.
  • The newly formed DNA strands rewind to form a double-helix spiral staircase shape once again.

Applications and Skills:

Application: PCR and Taq DNA Polymerase

Use of Taq DNA polymerase to produce multiple copies of DNA rapidly by the polymerase chain reaction (PCR).

  • PCR (polymerase chain reaction) is a laboratory technique that takes a single or few copies of DNA and amplifies them to generate millions or more copies of a particular DNA sequence.
  • When you collect DNA from different sources such as sperm samples or small drops of blood, there are usually very little usable cells to collect DNA.
  • Therefore, PCR is used to create enough DNA to be analyzed for investigations such as forensics or custody cases.
  • Once large quantities of the DNA have been created, other methods such as gel electrophoresis are used to analyze the DNA.